In situ observation of the initial adsorption process of heptylviologen cation radicals by slab optical waveguide spectroscopy synchronized with electrode potential modulation methods

In situ observation of absorption spectra of the heptylviologen cation radical (HV+·) was performed by slab optical waveguide (SOWG) spectroscopy utilizing indium-tin-oxide (ITO) electrodes. On application of potential sweep and potential step techniques from −300 to −600 mV (vs. Ag|AgCl), we observed the initial adsorption of HV+· on the ITO electrode. Two specific absorption bands were found at around 380 and 400 nm, which indicated that HV+· existed as both monomer and dimer on ITO with a monolayer or a few deposition layers. The change in the intensity and the peak position of the absorption spectra from adsorption species of HV+· was correlated with the electrode potential. These two absorption bands became incorporated in one broad band after a 30 s interval at −600 mV.